1. Field of the Invention
The present invention relates to a bus-protocol converting device and a bus-protocol converting method for a virtual memory bus master DMA system.
2. Description of the Related Art
SCSI (Small Computer System Interface), ATAPI (AT Attachment Packet Interface), USB (Universal Serial Bus) Mass Storage Class, IEEE (Institute of Electrical and Electronics Engineers) 1394 Serial Bus Protocol 2, and so on are available as storage bus standards. When an extension bus for a host device and a connection bus for a storage device are different from each other, they are connected with a bus-protocol converting device interposed therebetween.
A bus-protocol converting device having a FIFO (first-in first-out) memory and a DMA (direct memory access) controller is used in order to perform high-speed input/output of data between the devices connected to the buses having different standards.
For example, during conversion between a SCSI bus and an ATA-2 bus, data input/output is performed at high speed via a FIFO memory (e.g., refer to Japanese Unexamined Patent Application Publication No. 10-161972) and DMA (direct memory access) is performed between an IEEE 1394 bus and a SCSI bus in order to improve the performance of a data transfer operation (e.g., refer to Japanese Unexamined Patent Application Publication No. 2003-223411). In addition, a DMA transfer device that has FIFO and DMA between a primary bus and a secondary bus and that employs high-speed burst transfer has been proposed so as to achieve efficient data transfer (e.g., refer to Japanese Unexamined Patent Application Publication Nos. 2003-223411 and 2007-172510).
Data transfer using FIFO and DMA achieves high-speed burst transfer by performing DMA on addresses mapped in a contiguous address space.
Data access is executed by giving logical addresses with serial numbers (i.e., LBA: logical block addressing) to all minimum access units (i.e., units with a block length) of data and specifying a direction (read or write), a start LBA, and the number of blocks from an LBA by using command parameters.
A bus-protocol converting device incorporating a bus master DMA system is available to perform data transfer therein. In the bus master DMA system, a primary interface unit and a secondary interface unit transfer data by performing DMA access on a common memory for transfer and relay.